ABSTRACT Periodontal disease is a chronic inflammatory condition associated with gingival tissue breakdown and alveolar bone loss. No single organism has been implicated as the etiologic agent of periodontal disease, rather it is thought to be mediated by a dysbiotic oral community. Immune system dysregulation is hypothesized to be involved in driving the microbial community toward a dysbiotic state. As well, ecological succession and cell- to-cell interactions are hypothesized to play critical roles in community assembly in states of both health and disease. Molecular sequencing based methods provide exhaustive lists of organisms and genes present in a community such as that in the human oral cavity. However, these methods provide little information on how microbes are arranged in space in states of health and how the structure of complex oral microbial communities contributes to community function and disease progression. The goal of the research proposed here is to further develop a microbial imaging technology for mapping the systems level spatial structure of human oral microbial communities. Spectral imaging, combined with fluorescence in situ hybridization will be employed to map the spatial distribution of 8-15 different taxa of microbes in intact subgingival biofilms on teeth and in laboratory-grown mixed species cultures. An in vitro dental plaque microcosm model system will be developed to test the hypothesis that Fusobacterium nucleatum functions as an important bridge organism that unites early colonizing bacteria with late colonizing species. Dental plaque and saliva samples will be collected from 10 healthy volunteers after giving informed consent. Plaque samples will be used to seed microcosm cultures that will be grown in the laboratory. Oral microcosm communities will be supplemented with cultivated isolates of F. nucleatum to assay its effect on biofilm structure and complexity. This study will lay the groundwork for future controlled experiments to understand the effect that specific organisms have on the systems level spatial structure of complex oral microbial communities.